The present invention relates to devices for braking the rotation of reels of sheet material when the reeling operations are completed.
In particular, the present is designed for use in paper or cardboard machines where the paper or cardboard are reeled onto a reel spool or tambour roll. Thus, with the structure of the present invention it is possible to dissipate the rotary motion of the reeled body of sheet material, acquired during the reeling operation, until the sheet-material roll comes to a standstill.
It is already well known that in paper or cardboard machines the reeling mechanism for the finished paper or cardboard may include a so-called Pope cylinder driven in such a way as to have a peripheral velocity equal to the linear velocity of the completed web of sheet material. The paper or cardboard is reeled onto a so-called tambour roll or reel spool, with the paper or cardboard roll being urged, during the building thereof, against the Pope cylinder over which the web of the sheet material runs toward the roll which is being formed. During the reeling operation the tambour roll or reel spool is lodged in journal forks or on a roll carriage which is moved away from the Pope cylinder as the roll which is being formed increases in diameter. It is most common, at the present time, however, to support the reel spool so that it will roll upon supporting rails as the paper roll increases in diameter during reeling thereof. A suitable loading means maintains a sufficient contact pressure between the building sheet-material roll and the Pope cylinder.
It is of course known to provide reeling mechanisms with brakes for stopping the rotation of the completed roll. As a rule the braking operation is carried out at a fixed braking station to which the completed roll is transferred. The braking operations also may be performed by way of brake shoes fixed to the roll-displacing arms. In connection with reeling of relatively thick cardboard, it is known to use so-called floor brakes which stop the rotation of the roll by acting upon the surface thereof. With the exception of this latter type of construction, all known braking devices operate in such a way that the exterior surface at the end portions of the tambour roll or reel spool acts as a brake drum. This latter type of construction is of considerable disadvantage, however, in that the surface of the tambour roll is worn away and rendered useless after a relatively short period of time as a result of the frictional engagement with the brake shoe. A further drawback resides in the extremely large generation of heat at the part of the tambour roll or reel spool which is subjected to frictional engagement with the brake shoe. This latter drawback is of increasing significance with the ever-increasing width and speed of paper machines and increasing diameters of the rolls. This generation of heat may have a number of undesirable results among which are that the production of heat may loosen the shrinkage joint used in the tambour roll or it may destroy the rubber lining of the tambour roll.
Moreover, with the type of braking construction which is most commonly used, among those known in the prior art, which is to say that which has a fixed braking station, a large quantity of waste paper is produced because the outermost layers of the roll become loose as the roll rotates during the comparatively long time requried to transfer the roll to the braking station. This wastage of paper increases undesirably if for one reason or another relatively small roll sizes are provided as, for example, in the case where sample rolls are made when the operation of the machine is changed from one type of paper to another type of paper, inasmuch as in this case the transfer distance of such a roll which is smaller than the maximum diameter is even longer.
A further drawback of known braking devices resides in the fact that the braking takes place at the ends of the shell surface of the tambour roll, the portion thereof which must be used for engagement with the brake shoes reduces the space which is available for reeling of the paper.